Photographic light-sensitive materials generally comprise an electrically insulating support coated with photographic layers, and it often happens during their production that static charges are built up as they are rubbed against each other or other surfaces. The static charges so accumulated can cause many problems, the most serious of which is that the static charge so built up discharges to sensitize the light-sensitive emulsion layer before development so that when the film is developed, there occur punctate defects or dentritic or feathery streaks. These are generally called static marks, and detract considerably from the market value of a photographic film, or, at worst, destroy the value completely. It is easy to understand that if static marks are formed on medical or industrial X-ray film, for instance, they may lead to a dangerous misdiagnosis or judgement. Since this blemish becomes apparent for the first time only upon development of the film, it presents a very serious problem. Moreover, the accumulated static charge may induce secondary problems, such as deposition of dust on the film surface and/or failures to obtain uniform coating results.
While the aforesaid static charge is often built up in the course of production, handling and use of a photographic light-sensitive material, such static charge build-up in the course of production takes place, for example, due to friction between the photographic film and the roller assembly or the exfoliation of the emulsion layer from the support during the take-up or rewinding of the film. It also develops due to contact or peeling stress between the X-ray film and the mechanical parts of fluorescent sensitizing paper in the automatic camera. Another cause is contact with packaging materials. The static marks on the photographic light-sensitive material as caused by such accumulation of static charge become more conspicuous as the sensitivity of the light-sensitive material and/or the photographic processing speed are increased. Particularly, recent years have witnessed an increasing opportunity of photographic light-sensitive materials being exposed to very tortuous conditions such as an increased sensitivity of the light-sensitive materials themselves, high speed coating processes, high speed photographing, high speed automatic processing, etc., and these factors have been contributing to an increasing incidence of static marks.
To overcome these problems due to static electricity, it is desirable to incorporate an antistatic agent in photographic light-sensitive materials. However, all the antistatic agents commonly used in other fields of art cannot be used as such in photographic light-sensitive materials, but antistatic agents that can be used must meet several requirements peculiar to this field of art. Thus, in addition to a high static inhibiting action, the antistatic agent useful for photographic light-sensitive materials must have the following and other characteristics. Thus, it should not exert untoward effects on the photographic characteristics of light-sensitive materials, such as sensitivity, fog, grain properties, sharpness, etc. Secondly, there should not be an adverse influence on the film strength of the photographic light-sensitive material (i.e., the light-sensitive material should be resistant to abrasion and scratching). Thirdly, the antitack property of the light-sensitive material should not be adversely affected (i.e., the light-sensitive materials should not be made liable to stick to each other or to other surfaces). Moreover, the antistatic agent should not accelerate the fatigue of the processing solutions used for the photographic light-sensitive material. In addition, the antistatic agent should not be one that may reduce the bond strength between constituent layers of the photographic light-sensitive material. Thus, the application of an antistatic agent to photographic light-sensitive materials is subject to these and other restrictions.
An approach toward eliminating these troubles due to static electricity is that of increasing the electrical conductivity of the surfaces of photographic light-sensitive materials, to thereby dissipate the accumulated static charge in a short time before a discharge of the static charge takes place. Accordingly, various methods have been proposed for improving the electrical conductivity of the support and various coating layers superimposed thereon of the photographic light-sensitive material. Thus, the use of various hygroscopic agents and water-soluble inorganic salts, certain types of surfactants, polymers, etc., has been recommended. For example, U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291, 3,615,531, 3,753,716, 3,938,999, etc., mention such polymers; U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,972, 3,655,387, etc., refer to surfactants; and U.S. Pat. Nos. 3,062,700, 3,245,833, 3,525,621, etc., mention metal oxides, colloidal silica, etc.
However, many of these substances display properties specific only to some types of film supports and photographic compositions, and while these substances may produce satisfactory results with certain kinds of support films, photographic emulsions, and other photographic elements, they are quite useless or even exert adverse effects on photographic characteristics with other kinds of supports and photographic elements.
On the other hand, there also are many antistatic substances that cannot be used because they have adverse effects on photographic characteristics such as the sensitivity, fog, graininess, sharpness, etc., of the emulsion, notwithstanding the fact that they have excellent antistatic action. By way of illustration, polyethylene oxide compounds are generally known to have an antistatic effect, but tend to cause ill effects on photographic characteristics, such as increased fog, desensitization, graininess degradation, etc.
Particularly in regard to a direct X-ray-sensitive material for medical use, the support of which carries a radiographic emulsion layer on either side, it has been difficult to establish a technique for imparting an antistatic property thereto without sacrificing its photographic characteristics. Thus, it is very difficult to apply an antistatic agent to photographic light-sensitive materials, and the range of application has been limited.
Another approach toward obviating problems due to static charges in photographic light-sensitive materials is that of controlling the surface static potential of the light-sensitive material so as to minimize the generation of static electricity due to friction and contact. For example, attempts have been made to use fluorine-containing surfactants as described in British Pat. Nos. 1,330,356 and 1,524,621, U.S. Pat. Nos. 3,666,478 and 3,589,906, Japanese Patent Publication No. 26687/77, Japanese patent application (OPI) Ser. Nos. 46733/74 and 32322/76 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application open to public inspection"), and so on in photographic light-sensitive materials for the above-mentioned purposes. However, since the static charge characteristics of photographic light-sensitive materials containing such fluorine-containing surfactants are dependent on the characteristics of the surfactant used, such as formation of a unimolecular film, they vary markedly with different processing conditions to which such photographic light-sensitive materials are subjected in the course of their production. The result is that uniform products having uniform static charge characteristics cannot be produced on a consistent basis. For example, the static charge characteristics of products vary widely in response to the temperature and humidity conditions used in the stages where the respective layers of the photographic light-sensitive materials are formed or the temperature, humidity, or/and drying time used in the drying stage subsequent to the coating processes. Therefore, while satisfactory products are obtained at times, products with quite poor static charge characteristics are produced at other times, thus presenting a serious obstacle to effective quality control. Thus, said fluorine-containing surfactants that have been used have the foregoing and other disadvantages.
To overcome the above-mentioned disadvantages of fluorine-containing surfactants, attempts have also been made to utilize fluorine-containing polymers in photographic light-sensitive materials. For example, U.S. Pat. No. 4,266,015 teaches the use of an emulsion (latex) of a homopolymer of a fluorine-containing alcohol acrylic or methacrylic acid ester or of a copolymer of such ester monomer with some other monomer and U.S. Pat. No. 4,299,524 discloses the use of a copolymer of said fluorine-containing monomer with a polyethylene oxide chain-containing monomer. Japanese Patent Publication No. 15376/82 teaches the use of a copolymer of a fluorine-containing monomer such as said fluorine-containing monomer, a fluorine-containing carboxylic acid vinyl ester, a fluorine-containing vinyl ether, or a fluorine-substituted olefin with a quaternary nitrogen-containing monomer, while U.S. Pat. No. 3,753,716 teaches the use of a terpolymer of a fluorine-containing alcohol maleic acid ester, maleic acid, and another monomer in the photographic light-sensitive material (particularly in its surface layer). When such a fluorine-containing polymer is applied to a photographic light-sensitive material, the surface static potential of the light-sensitive material can be modulated to a certain extent so that the generation of static charges due to friction or contact can be somewhat decreased. Moreover, this technique overcomes, in some measure, the above-mentioned disadvantages of fluorine-containing surfactants, namely, the disadvantage that the static charge characteristics of light-sensitive materials vary a great deal with production conditions and the disadvantage that said characteristics age or deteriorate with time. However, photographic light-sensitive materials incorporating such fluorine-containing polymers have various drawbacks, for example, in respect of said static charge characteristics or in regard to photographic characteristics and film physical properties which are important factors in photographic light-sensitive materials, and these drawbacks detract considerably from their market value so that virtually these polymers cannot be used in photographic light-sensitive materials.
The layer of a photographic light-sensitive material which contains the fluorine-containing polymer emulsion as described in U.S. Pat. No. 4,266,015 is so tacky that there tends to occur an adhesion between the emulsion layers or between the emulsion layer and the backing layer of the material, and once adhered to each other, they cannot be separated, or if they can be separated, a conspicuous adhesion scar remains. Moreover, the polymer-containing layer of the photographic light-sensitive material tends to be marred by frictional contact with other surfaces or by scratching and such mars detract from the market value of photographic light-sensitive materials in a remarkable degree. On the other hand, the fluorine-containing polymers described in U.S. Pat. No. 4,299,524, Japanese Patent Publication No. 15376/82, and U.S. Pat. No. 3,753,716 must be added in substantial amounts to photographic light-sensitive materials, for they are quite deficient in their ability to control the static potential. This means not only an increased production cost, but also produces adverse effects on photographic characteristics such as decreased sensitivity, reduced density, and fog as well as on film properties such as liability to stick, or to be marred. Therefore, these polymers cannot be utilized in photographic light-sensitive materials.
To obviate the above-mentioned disadvantages of fluorine-containing polymers, British Pat. No. 2,080,559 and U.S. Pat. No. 4,362,812 teach a fluorine-containing polymer obtainable by copolymerizing a hydrophobic fluorine-containing monomer, which is a styrene derivative, with a water-soluble monomer. This fluorine-containing polymer enables one to adjust the static charge potential with a reduced amount as compared with the first-mentioned fluorine-containing polymer so that the production cost can be reduced. Moreover, the above-mentioned adverse effects on photographic characteristics such as decreased sensitivity, reduced density, and fogging, and on film properties such as liability to stick or be easily marred can be alleviated.
However, the sensitivity of photographic light-sensitive materials has been on a steady increase in recent years, as epitomized by the development of color reversal film and color negative film with an ISO sensitivity of 1600.
The photographic characteristics of these high sensitivity photographic light-sensitive materials are very delicate and the addition of even a minor impurity may alter the photographic characteristics in a remarkable measure. Therefore, when an antistatic agent is to be added to such a high sensitivity photographic material, the antistatic agent must not only be inert to the photographic emulsion but must also be capable of producing a potent antistatic effect even when used in a small amount.
The above-mentioned fluorine-containing polymer realizes a sufficient antistatic effect without affecting the photographic characteristics as long as it is used in a low sensitivity photographic light-sensitive material, but it cannot be used with respect to the above-noted recent high sensitivity photographic materials. Thus, the untoward effects on photographic characteristics such as decreased sensitivity, reduced density, and fogging are inevitable and unavoidable with the polymer just mentioned insofar as it is applied to high sensitivity photographic materials.
Moreover, the development process has also become more rapid than ever before, and today photographic light-sensitive materials are developed under remarkably tortuous conditions.
As mentioned in regard to the recent trend toward an ever increasing sensitivity of photographic materials, photographic characteristics are becoming more and more delicate so that, in this regard too, the antistatic agent must not only be inert to the photographic emulsion but be capable of affording a sufficient antistatic effect while being used in as small an amount as possible. When a static-inhibited photographic light-sensitive material incorporating the above fluorine-containing polymer is subjected to rapid development, its photographic characteristics are adversely affected. Therefore, the above-mentioned fluorine-containing polymer cannot be utilized in conjunction with rapid development materials.
In addition, high speed coating technology has recently been applied to the production of photographic light-sensitive materials as well, and, mainly during take-up of the photographic light-sensitive material, the surface of the light-sensitive material is subjected to high pressure. Under the circumstances, it has become necessary that the surface of the photographic light-sensitive material will not stick, but rather will be low in tackiness.
In earlier low speed production processes, the surface of the photographic light-sensitive material was only subject to moderate pressure and, therefore, even the above-mentioned fluorine-containing polymer was sufficient to ensure the necessary antitack property. However, with the recent development of high speed coating technology, the surface of the photographic light-sensitive material has come to be subjected to very substantial pressure, so that the fluorine-containing polymer just mentioned is unable to ensure a sufficient antitack property.
In this connection, it is important to understand that the fluorine-containing polymers mentioned hereinbefore belong to the category of "random copolymers". Generally, a random copolymer is a copolymer in which two or more kinds of monomer units are randomly arranged. In the production of a random copolymer, the mixing of the constituent units takes place on a monomer scale so that a homogeneous polymer compound tends to be obtained. However, because of the interactions between the constituent monomers, for instance, it is in many cases impossible to obtain the characteristics typical of the respective homopolymers. On the other hand, a "blending" of dissimilar polymers does not give a uniform composition in many cases but the respective polymers form distinct phases so that the phenomenon called phase separation takes place. In contrast to the above polymers, the so-called block polymer in which a polymer chain consisting of monomer units of a given kind is connected to a polymer chain consisting of monomer units of another kind in a linear fashion is characterized in that because the two dissimilar polymer segments are joined together by chemical bonding, it does not undergo as serious a phase separation as does a polymer blend, but does undergo the so-called microphase separation, assuming a multiphase structure. This is an outstanding feature which is not found in random copolymers and polymer blends.
Various characteristics of block polymers are generally described, for example, in the Society of High Polymer Chemistry: Polymer Alloys (Tokyo Kagaku Dojin, 1981); R. J. Ceresa, Block and Graft Polymerization, Vol. 1 (John Wiley & Sons, 1973); and Yamashita et al., Oil Chemistry, Vol. 29, pp. 219-225 (1980).
Paying attention to these various characteristics of block polymers, the present inventors conducted an intensive research to develop an antistatic agent free of the above disadvantages of fluorine-containing random copolymers. As a result, it was found surprisingly that the use of a block polymer derived from a hydrophobic fluorine-containing monomer and a hydrophilic monomer as an antistatic agent in the photographic light-sensitive material results in complete elimination of all the aforesaid disadvantages of said fluorine-containing random copolymers.